A charge pump circuit with leakage current compensation function

Abstract

The present invention provides a charge pump circuit with a leakage current compensation function, comprising: a charge pump circuit, a filter circuit, a leakage current detection circuit, a leakage current compensation algorithm and a leakage current compensation circuit; the charge pump circuit converts a voltage signal at an input end into a current signal, and then integrates the current signal through the filter circuit to convert it into a voltage signal Vctrl; the leakage current detection circuit is used to detect the polarity of the leakage current of the Vctrl node, if the output of the leakage current detection circuit is low, it indicates that the leakage current is a negative value; if the output of the leakage current detection circuit is high, it indicates that the leakage current is a positive value; the leakage current compensation algorithm adjusts the compensation current output by the leakage current compensation circuit according to the polarity of the leakage current; if the leakage current is a positive value, the compensation current is reduced; if the leakage current is a negative value, the compensation current is increased.

Description

Technical Field

[0001] The invention belongs to the field of electronic circuits, in particular to the field of phase-locked loops and clock data recovery circuits. Background Art

[0002] Charge pump circuits are widely used in phase-locked loop (PLL) and clock data recovery (CDR) circuits. Figure 1 The typical PLL / CDR system structure diagram is given. The function of the charge pump is to convert the voltage signal UPB / DN at the input end into a current signal, and then integrate the current signal through the filter at the output end, and finally convert it into a stable voltage signal Vctrl to control the subsequent voltage controlled oscillator (VCO).

[0003] The leakage current of the charge pump mainly comes from two aspects. On the one hand, as the integrated circuit manufacturing process becomes more and more advanced, the MOS tube gate oxide layer becomes thinner and thinner, and the subthreshold voltage becomes lower and lower, the device itself will have a certain leakage current. Figure 1 Ileak1~Ileak4 in the figure all represent this leakage current. Among them, the leakage current Ileak3 of C1 is the largest, because the capacitance value of C1 is usually large. In order to save chip area, C1 is generally implemented with MOS capacitors, and the leakage current is the most serious. On the other hand, in high-speed circuit design, differential switch charge pumps are often used, such as Figure 2 As shown. Due to the process mismatch or insufficient voltage margin in the production process, the differential switch tubes M1 / M2 and M3 / M4 cannot be completely switched. When the charging signal UP (UPB is the inverted signal of UP) and the discharging signal DN (DNB is the inverted signal of DN) are both low, the charge pump should not have an external charging and discharging current. However, due to the incomplete switching of M1 / M2 and M3 / M4, there is still an external charging current Ileakup and an external discharging current Ileakdn, and the final output leakage current is equal to Ileakup-Ileakdn.

[0004] The leakage current of the charge pump will cause the Vctrl voltage fluctuation to increase, increase the jitter of the PLL and CDR, reduce the system performance, and in severe cases, cause the overall function of the system to fail.

[0005] Technical solutions similar to the present invention include [1, 2]. Solution [1] uses a closed-loop clamping amplifier Ab to make the voltage VC1 on the capacitor C1 follow the control voltage Vctrl, that is, the leakage current of the capacitor C1 is compensated by the output current of the clamping amplifier Ab. The disadvantage of this solution is that it can only compensate for the leakage current of the capacitor C1 in the filter, but cannot compensate for the leakage current of the switch tube in the charge pump.

[0006] Solution [2] uses MOS tube T3 to detect the size of VC voltage to generate compensation current, and then sends the compensation current back to the VC terminal through the current mirror formed by T2 and T1 to compensate for the leakage current. The disadvantage of this solution is that it can only compensate for the leakage current of C1, but cannot compensate for the leakage current of the switch tube in the charge pump. Another disadvantage is that the leakage current detection method depends on the characteristics of T3 tube and has low accuracy.

[0007] That is to say, the prior art can only compensate for the leakage current of the capacitor in the filter, but cannot compensate for the leakage current of the charge pump switch tube. Summary of the invention

[0008] The main technical problem to be solved by the present invention is to propose a charge pump circuit with leakage current compensation function, which can simultaneously compensate for the leakage current of the charge pump switch tube and the leakage current of the capacitor in the filter.

[0009] In order to solve the above technical problems, the present invention provides a charge pump circuit with leakage current compensation function, including: a charge pump circuit, a filter circuit, a leakage current detection circuit, a leakage current compensation algorithm and a leakage current compensation circuit;

[0010] The charge pump circuit converts the voltage signal at the input end into a current signal, and then integrates the current signal through the filter circuit to convert it into a voltage signal Vctrl;

[0011] The leakage current detection circuit is used to detect the polarity of the leakage current of the Vctrl node. If the output of the leakage current detection circuit is low, it indicates that the leakage current is negative; if the output of the leakage current detection circuit is high, it indicates that the leakage current is positive;

[0012] The leakage current compensation algorithm adjusts the compensation current output by the leakage current compensation circuit according to the polarity of the leakage current; if the leakage current is a positive value, the compensation current is reduced; if the leakage current is a negative value, the compensation current is increased.

[0013] In a preferred embodiment: after the leakage current compensation algorithm increases or decreases the compensation current, the leakage current detection circuit detects the polarity of the leakage current of the Vctrl node again; if the polarity of the leakage current has not reversed, the compensation current is increased or decreased again until the polarity of the leakage current is reversed.

[0014] In a preferred embodiment: the leakage current detection circuit includes shutoff switches Kp and Kn, and the shutoff switches Kp and Kn are controlled by a PD shutoff signal. When the PD shutoff signal is 1, the shutoff switches Kp and Kn are closed, and the leakage current detection circuit is turned off; when the PD shutoff signal is 0, the shutoff switches Kp and Kn are disconnected, and the leakage current detection circuit works normally.

[0015] In a preferred embodiment: the leakage current compensation circuit is a mirror current source array, each current source is controlled by a switch; the leakage current compensation circuit selects to open or close the switches of different current sources according to the gear control of the leakage current compensation algorithm to adjust the size of the compensation current Icomp.

[0016] In a preferred embodiment: when all switches of the leakage current compensation circuit are turned on or off, the polarity of the leakage current still does not reverse, then the leakage current compensation algorithm sets the failure flag to 1 and sets the PD shutdown signal to 1.

[0017] In a preferred embodiment: when the polarity of the leakage current is reversed, the leakage current compensation algorithm sets the success flag to 1 and sets the PD shutdown signal to 1.

[0018] In a preferred embodiment: the leakage current detection circuit includes an operational amplifier circuit and a current mirror circuit connected to the output stage of the operational amplifier circuit;

[0019] And the output end of the operational amplifier circuit and the output end of the current mirror circuit are connected to the positive electrode and the negative electrode of the comparator.

[0020] In a preferred embodiment: the output terminal and the reverse input terminal of the operational amplifier circuit are short-circuited and connected to the Vctrl node to form a unit gain negative feedback loop; the non-inverting input terminal of the operational amplifier circuit is connected to the common mode voltage Vcm, which is the middle value of the normal working range of the Vctrl voltage.

[0021] In a preferred embodiment: the leakage current detection circuit is used to detect the leakage current of all cells connected to the Vctrl node.

[0022] In a preferred embodiment: the charge pump circuit is a single-ended switching charge pump or a differential switching charge pump.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1. The present invention provides a charge pump circuit with a leakage current compensation function, which accurately compensates for all types of leakage currents in the charge pump through three steps of detection-judgment-compensation.

[0025] 2. The present invention provides a charge pump circuit with leakage current compensation function. A closed-loop two-stage operational amplifier is used in the leakage current detection circuit to clamp the Vctrl voltage equal to Vcm, so that the leakage current of all units connected to the Vctrl node will be detected together. Then, the polarity of the leakage current is detected by mirroring the current of the output stage of the two-stage operational amplifier, and then it is determined whether the compensation current should be increased or decreased. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a typical PLL / CDR system structure diagram;

[0027] Figure 2 A typical differential switch charge pump and leakage current schematic diagram;

[0028] Figure 3 It is a circuit diagram of prior art solution 1;

[0029] Figure 4 It is a circuit diagram of prior art solution 2;

[0030] Figure 5 It is a module diagram of a preferred embodiment of the present invention;

[0031] Figure 6 A leakage current detection circuit diagram in a preferred embodiment of the present invention;

[0032] Figure 7 is a flow chart of the leakage current compensation algorithm of the present invention;

[0033] Figure 8 This is a schematic diagram of the leakage current compensation circuit of the present invention. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] refer to Figure 5-Figure 8 , this embodiment provides a charge pump circuit with a leakage current compensation function, including: a charge pump circuit, a filter circuit, a leakage current detection circuit, a leakage current compensation algorithm and a leakage current compensation circuit;

[0038] The charge pump circuit converts the voltage signal at the input end into a current signal, and then integrates the current signal through the filter circuit to convert it into a voltage signal Vctrl;

[0039] Specifically, the charge pump circuit is composed of a charging current source Iup, a discharging current source Idn, a charging switch K1, and a discharging switch K2, wherein K1 and K2 can be either Figure 1 The single-ended switch in Figure 2 The differential switch in the circuit. The charging current source Iup is connected to the Vctrl node through the charging switch K1, and the discharging current source Idn is connected to the Vctrl node through the discharging switch K2. UP is the charging switch enable signal, and DN is the discharging switch enable signal. The filter circuit is composed of resistor R1, capacitor C1 and C2. C2 is directly connected to the Vctrl node, and C1 is connected to the Vctrl node through R1.

[0040] The leakage current detection circuit is used to detect the polarity of the leakage current of the Vctrl node. If the output of the leakage current detection circuit is low, it indicates that the leakage current is negative; if the output of the leakage current detection circuit is high, it indicates that the leakage current is positive;

[0041] The leakage current compensation algorithm adjusts the compensation current output by the leakage current compensation circuit according to the polarity of the leakage current; if the leakage current is a positive value, the compensation current is reduced; if the leakage current is a negative value, the compensation current is increased.

[0042] Figure 6 The schematic diagram of the leakage current detection circuit of this scheme is given. MOS tubes M1~M8 constitute a typical two-stage operational amplifier. The first stage of the two-stage operational amplifier consists of M2~M6, and the output stage consists of M7 and M8. M1 is a bias circuit, and R1 and C1 are used to compensate for loop stability. The gate of MOS tube M3 is the inverting input terminal of the two-stage operational amplifier, the gate of MOS tube M4 is the non-inverting input terminal of the two-stage operational amplifier, and the connection point of MOS tubes M7, M8 and capacitor C1 is the output terminal of the two-stage operational amplifier. In this structure, the output terminal and the inverting input terminal of the two-stage operational amplifier are short-circuited and connected to Figure 5The Vctrl node in it forms a unity-gain negative feedback loop. The non-inverting input terminal of the two-stage operational amplifier is connected to the common-mode voltage Vcm, and Vcm is the middle value of the normal operating range of the Vctrl voltage. MOS transistor M9 is a 1:1 current mirror of M7, and M10 is a 1:1 current mirror of M8. The output node of the two-stage operational amplifier is also connected to the non-inverting input terminal of the comparator, and the connection point of the drains of M9 and M10 is connected to the inverting input terminal of the comparator. POL is the output of the comparator and also the output of the entire leakage current detection circuit. Kp and Kn are turn-off switches controlled by the PD turn-off signal. When PD is 1, the entire leakage current detection circuit is turned off. When PD is 0, the leakage current detection circuit operates normally.

[0043] The current mirror ratio of M7 / M8 and M9 / M10 in the leakage current detection circuit does not necessarily have to be a 1:1 relationship and can be a 1:N relationship. In this embodiment, a 1:1 mirror relationship is adopted for simplicity. And the structure of the two-stage operational amplifier can be changed, which belongs to a simple replacement in this embodiment.

[0044] The leakage current detection circuit of this solution detects the magnitude of the leakage current at the Vctrl node. The leakage currents of all units connected to the Vctrl node, including Figure 5 the leakage currents of R1, C2, K1, K2 in it and C1 connected to Vctrl through R1 will all be detected together. Therefore, this solution can compensate for all leakage currents.

[0045] The working principle of the leakage current detection circuit is as follows: During the leakage current compensation process, the turn-off signal PD is 0, and the switches Kp and Kn are turned off, and the leakage current detection circuit operates normally. Vctrl is equal to Vcm due to the clamping effect of the closed-loop operational amplifier. Define the currents flowing through MOS transistors M7 to M10 as IM7 to IM10 respectively. Since there is a leakage current at the Vctrl node, IM7 is not equal to IM8. Also, because M9 and M10 mirror the currents of M7 and M8 respectively by 1:1, IM9 is not equal to IM10. However, because V1 is a high-impedance node and there is no current discharge path, finally, due to the channel length modulation effect of the MOS transistor, the voltage of V1 will deviate from the Vctrl voltage. When IM9 > IM10, V1 is greater than Vctrl, and the POL output is low, indicating that the leakage current is negative; conversely, when IM9 < IM10, V1 is less than Vctrl, and the POL output is high, indicating that the leakage current is positive. After the leakage current compensation process is completed, the turn-off signal PD is set to 1, and the switches Kp and Kn are turned on, and the entire leakage current detection circuit is turned off.

[0046] The flow of the leakage current compensation algorithm of this solution is as Figure 7As shown. After the system is powered on, the shutdown signal PD is set to 0, the leakage current detection circuit starts working, the charge pump charge and discharge control signals UP and DN are forced to 0, and the system is stabilized after waiting for T1 time. The leakage current detection circuit detects the polarity of the leakage current. If POL is low, it means that the leakage current is negative, then the gear of the leakage current compensation circuit is increased, thereby increasing the compensation current; if POL is high, it means that the leakage current is positive, then the gear of the leakage current compensation circuit is reduced, thereby reducing the compensation current. After adjusting the gear of the leakage current compensation circuit, wait for T1 time again to stabilize the system, and then judge the POL polarity again. This cycle continues until the polarity of POL is reversed, indicating that the compensation algorithm has found the optimal compensation gear. Fix this gear, set the PD signal to 1, turn off the leakage current detection circuit, release the UP and DN signals of the charge pump, set the success flag to 1, and the process ends. In the process of searching for the optimal compensation gear, if the maximum or minimum value of the compensation gear is reached and the POL polarity has not reversed, it indicates that the search for the optimal compensation gear has failed, the failure flag is set to 1, and the PD signal is set to 1 at the same time, turning off the leakage current detection circuit and releasing the UP and DN signals of the charge pump.

[0047] In the leakage current calibration process of this scheme, the UP and DN signals are set to 0, that is, Figure 5 The switches K1 and K2 in the circuit are both in the off state. At this time, except for the leakage current of the switches K1 and K2, the charge pump will not charge or discharge the filter.

[0048] Figure 8 The schematic diagram of the leakage current compensation circuit of this scheme is given. M0~M4 constitute a mirror current source array, and switches K1~K4 control the on and off of each current source. Ib is the bias current. The leakage current compensation circuit will choose to open or close the switches of different current sources according to the gear control of the compensation algorithm to adjust the size of the compensation current Icomp. This scheme adopts a PMOS tube current source array, and an NMOS tube current source array can also be adopted as an alternative. Of course, it can also be any other type of current source array, such as a common source and common gate current source. In addition, the leakage current compensation circuit of this scheme adopts a total of 4 current sources to form an array, and the number of channels can be flexibly increased or decreased according to the needs of compensation accuracy.

[0049] The above is only a preferred specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any technician familiar with the technical field who uses this concept to make non-substantial changes to the present invention within the technical scope disclosed by the present invention shall be deemed to infringe the protection scope of the present invention.

Claims

1. A charge pump circuit with leakage current compensation function, characterized in that include: A charge pump circuit, a filter circuit, a leakage current detection circuit, a leakage current compensation algorithm and a leakage current compensation circuit; The charge pump circuit converts the voltage signal at the input end into a current signal, and then integrates the current signal through the filter circuit to convert it into a voltage signal Vctrl; The leakage current detection circuit is used to detect the polarity of the leakage current of the Vctrl node. If the output of the leakage current detection circuit is low, it indicates that the leakage current is negative; if the output of the leakage current detection circuit is high, it indicates that the leakage current is positive; The leakage current compensation algorithm adjusts the compensation current output by the leakage current compensation circuit according to the polarity of the leakage current; if the leakage current is positive, the compensation current is reduced; if the leakage current is negative, the compensation current is increased; The leakage current detection circuit includes a shutoff switch Kp and a shutoff switch Kn, and the shutoff switches Kp and Kn are controlled by a PD shutoff signal. When the PD shutoff signal is 1, the shutoff switches Kp and Kn are closed, and the leakage current detection circuit is turned off; when the PD shutoff signal is 0, the shutoff switches Kp and Kn are disconnected, and the leakage current detection circuit works normally; The leakage current detection circuit includes an operational amplifier circuit and a current mirror circuit connected to the output stage of the operational amplifier circuit; The output end of the operational amplifier circuit and the output end of the current mirror circuit are connected to the positive electrode and the negative electrode of the comparator; The output terminal and the reverse input terminal of the operational amplifier circuit are short-circuited and connected to the Vctrl node to form a unit gain negative feedback loop; the non-inverting input terminal of the operational amplifier circuit is connected to the common mode voltage Vcm, which is the middle value of the normal working range of the Vctrl voltage.

2. The charge pump circuit with leakage current compensation function according to claim 1, characterized in that: After the leakage current compensation algorithm increases or decreases the compensation current, the leakage current detection circuit detects the polarity of the leakage current of the Vctrl node again; if the polarity of the leakage current has not reversed, the compensation current is increased or decreased again until the polarity of the leakage current is reversed.

3. The charge pump circuit with leakage current compensation function according to claim 1, characterized in that: The leakage current compensation circuit is a mirror current source array, each current source is controlled by a switch; the leakage current compensation circuit selects to open or close the switches of different current sources according to the gear control of the leakage current compensation algorithm to adjust the size of the compensation current Icomp.

4. The charge pump circuit with leakage current compensation function according to claim 3, characterized in that: When all switches of the leakage current compensation circuit are turned on or off, and the polarity of the leakage current still does not reverse, the leakage current compensation algorithm sets the failure flag to 1 and sets the PD shutdown signal to 1.

5. The charge pump circuit with leakage current compensation function according to claim 4, characterized in that: When the polarity of the leakage current is reversed, the leakage current compensation algorithm sets the success flag to 1 and sets the PD shutdown signal to 1.

6. The charge pump circuit with leakage current compensation function according to claim 1, characterized in that: The leakage current detection circuit is used to detect the leakage current of all units connected to the Vctrl node.

7. A charge pump circuit with leakage current compensation function according to any one of claims 1 to 6, characterized in that: The charge pump circuit is a single-ended switching charge pump or a differential switching charge pump.

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